ABB RELION RET670 Applications Manual page 336

Section 8
Impedance protection
330
Parallel line applications
This type of networks are defined as those networks where the parallel transmission
lines terminate at common nodes at both ends.
The three most common operation modes are:
1. parallel line in service.
2. parallel line out of service and grounded.
3. parallel line out of service and not grounded.
Parallel line in service
This type of application is very common and applies to all normal sub-transmission
and transmission networks.
Let us analyze what happens when a fault occurs on the parallel line see figure 154.
From symmetrical components, we can derive the impedance Z at the relay point for
normal lines without mutual coupling according to equation 208.
U
ph
Z = =
- +
Z Z I
0 1 ph
+ ×
I 3I
ph 0
×
3 Z
1
EQUATION2311 V1 EN-US
V
ph
Z =
-
Z Z
0
+ ×
I 3I
ph 0
×
3 Z
EQUATION1275 V3 EN-US
Where:
V is phase to ground voltage at the relay point
ph
I is phase current in the faulty phase
ph
3I is ground fault current
0
Z is positive sequence impedance
1
Z is zero sequence impedance
0
U
ph
×
3I K
0 N
V
ph
=
I
+ ×
I 3 K
1 ph N
0
1
1MRK 504 163-UUS A
GUID-9980E92C-EDB1-4E0C-A4BD-167C896199A1 v1
GUID-F792E7FD-2265-4250-9026-1F03039FB0B5 v1
(Equation 208)
(Equation 208)
Transformer protection RET670 2.2 ANSI
Application manual